Wrap render library lines into a function called renderLibrary. Call the function and pass in books array at the end of the script.
Add #add-book form so the user can add a book. Add jQuery function .submit() so on submit the book in the form is added to the books array and then added to the DOM with another instance of the underscore book template.
Restructure functions. Put main function call at the bottom of the functions. #codecleanup